This invention relates to pencil, eraser and sharpener combinations. More particularly, this invention relates to an improved disposable pencil, eraser, and sharpener structure, and to an improved method of using the sharpener to effect sharpening of a pencil lead.
In general, lead pencils may be classified as either disposable pencils or mechanical pencils. Disposable pencils are inexpensive pencils which are intended to be thrown away after the lead is consumed and typically include a lead core (or more commonly a graphite marking material contained in a binder) enclosed in a groove between two substantially semicylindrical wood casings cemented to form a unit. Such pencils usually have an eraser fixed at one end. These "wood case" lead pencils are sharpened to expose the lead, and after a number of sharpenings are consumed and must be thrown away as they have no further use. The advantage of disposable pencils is that they are inexpensive, very functional and easy to use. Mechanical pencils on the other hand are not disposable and are intended to use replaceable pencil leads. In these pencils, the lead is axially movable within the pencil body to expose the lead and after one lead is consumed, it is replaced by another. Such replaceable lead type mechanical pencils are generally not made disposable because the cost of manufacturing the pencil dictates that it be reusable with multiple replaceable lead if it is to be commercially feasible.
This invention is concerned with the disposable type pencils. Specifically, it has been the primary objective of this invention to provide a disposable type lead pencil which has all of the desirable physical and functional characteristics of a disposable pencil, but with the additional feature of a built-in pencil sharpener contained interiorly of the pencil body. Heretofore, all commercial disposable pencils of which we are aware have required auxiliary pencil sharpeners or sharpening devices for resharpening and exposing the lead of the pencil. It has been the primary objective of this invention therefore to build in the sharpener of a disposable pencil so as to eliminate the need for that auxiliary device.
Heretofore, there have been innumerable attempts to develop a pencil having a built-in sharpener, but so far as we are aware, all such attempts have involved the addition of a sharpener to a replaceable lead type mechanical pencil. The construction of these mechanical pencils, to which sharpeners were added, was always too complex and expensive to permit of their being disposable after consumption of a single lead contained within the pencil, and accordingly they were not designed for or ever intended to be disposable. But, it was in the area of disposable pencils where there was a need for a built-in sharpener. Accordingly, so far as we know, although there have been numerous attempts to create a pencil having a built-in sharpener, none of these attempts was ever commercially acceptable or met the need for a disposable pencil having a built-in sharpener.
The prior art built-in sharpener mechanical pencils of which we are aware suffered not only from being complex and expensive to manufacture, but they also suffered from the fact that most of them required very tight tolerances between the parts of the pencil, which tight tolerances also added to the expense of the product by precluding as a practical matter complete machine manufacture and assembly of the product.
Examples of prior art complex expensive mechanical pencils which have built-in sharpeners but which are too expensive and complex to be practical are found in U.S. Pat. Nos. 1,719,976 and 1,849,914, and British Pat. No. 679,264. In theory, these patents all appear to disclose practical self-sharpener mechanical pencils, but in practice the cost of manufacturing these mechanical pencils and the difficulty of manufacturing them in any appreciable volume with appropriate controls to assure operability preclude their practicality. Their designs also preclude their being manufactured and sold as disposable pencils.
Another common shortcoming of most prior art mechanical pencils has been the slowness with which they sharpen the pencil leads and the difficulty of using the sharpener. Many of these pencils rely upon withdrawal of the lead into the interior of the pencil and then rotation of the lead relative to the sharpener to effect the sharpening. This process is not only slow but is difficult to practice. Additionally, if the sharpener is an abrasive rather than a scraper, as for example in U.S. Pat. No. 1,327,038, the rotation of the abrasive sharpener relative to the lead cuts annular striations in the lead which very markedly reduces the strength of the lead and causes it to be easily broken when writing pressure is applied to it.
Another common shortcoming of very nearly all mechanical pencils of the type which includes a built-in sharpener is that they permit the filings to fall from the pencil onto the work surface or into the pockets or onto the hands of the person using the pencil. The above identified four patents are all subject to this shortcoming. One mechanical pencil which is not subject to this problem because of its provision of a seal around the sharpener of the pencil is Kohut U.S. Pat. No. 2,680,426. But, we have found that the seals of the Kohut patent create other problems. In the Kohut patent, the seals are disclosed as flat rubber or plastic washers. If those rubber washers or seals are sufficiently tight as to prevent leaking of the filings they will tend to break the lead and if loose, the filings will pass through the seal. Furthermore, we have found that flat rubber seals are ineffective as seals because the binder used in conventional leads is too abrasive to permit the lead to slip through a flat rubber seal without lead breakage if the seal is sufficiently tight to prevent leakage, and if the seal is made loose so as to avoid breakage of the lead, then it permits the lead filings to escape and create a cleanliness problem.
Accordingly, it has been another objective of this invention to provide a pencil having a built-in sharpener contained within a sealed chamber of the pencil from which the lead filings cannot escape.
It has been still a further objective of this invention to provide an improved disposable pencil, eraser and sharpener combination in which the lead sharpener is disposed within an enclosed sealed chamber such that filings cannot escape from the chamber either during sharpening or when the lead's writing end is moved forwardly into a writing attitude outside of the chamber. The construction of the sharpener and chamber are such that the chamber holds all of the lead filings for the full length of pencil lead without interference with the abrasive sharpening action. The only seals which we have found to be effective are those which have multiple spaced contact with the pencil lead such as sponge or foam rubber, or multiple stacked and spaced plys of resilient sealing material. We have further found that to be effective the seal must have the "memory" and resilient characteristic of latex rubber so as to fully and quickly close when the lead is withdrawn into the interior of the sealed chamber and yet maintain sealing contact with the lead when the lead is pushed forwardly through the seal.
Another objective of this invention has been to provide an improved disposable pencil eraser and sharpener structure incorporating a unique sharpener and an improved method for sharpening the lead of the pencil. In the practice of this method, the lead is initially retracted into the interior of the pencil and is then linearly and axially reciprocated relative to an abrasive sharpener with the abrasive having only longitudinal cutting contact with the pencil lead.